. The book of photography; practical, theoretical and applied. fluorescenceon the prepared screen, and, upon lookingthrough the lens in a dark room, a minia-ture bombardment is seen to be going onthere. Tiny points of light appear, as theelectrified particles of matter strike thescreen, and the appearance is like that ofa continual discharge of tiny sparks. TheSpinthariscope principle has also beenapplied to a slide which, can be viewedon the stage of an ordinaxy microscope. Concluding Hints. It may be useful to give definite instruc-tions for making a fluorescent screen. Purebarium platino-cy
. The book of photography; practical, theoretical and applied. fluorescenceon the prepared screen, and, upon lookingthrough the lens in a dark room, a minia-ture bombardment is seen to be going onthere. Tiny points of light appear, as theelectrified particles of matter strike thescreen, and the appearance is like that ofa continual discharge of tiny sparks. TheSpinthariscope principle has also beenapplied to a slide which, can be viewedon the stage of an ordinaxy microscope. Concluding Hints. It may be useful to give definite instruc-tions for making a fluorescent screen. Purebarium platino-cyanide is reduced to a tinepowder and mixed with megilp, as used foroil painting. The mixture is applied with abrush to a sheet of glass of the desii-ed size,securing an even coating about J^. in. waiting for the mixture to dry asheet of very thin ebonite is laid over it, or,if this cannot be obtained, black paper,pressing lightly into contact. In use, theebonite or black paper side is placed nearestto the tube, the glass side being towards the. Fiir. .lli-1. -Photogkaph printed by DiKKtT LightOF Radium. observer. Another method is to stretch asheet of stout parchment on a frame, and,after coating it with thick celluloid varnish,to dust the powdered platino-cyanide overthe sticky surface and allow to dry. Whenperfectly dry, the resulting screen may begiven a coating of thin celluloid varnish,which must be applied gently and with care,so . a? not to damage the surface. Thevarnish may be made by dissolving cuttingsof old celluloid films—from which the gelatinehas been removed—in acetone, till a viscidliquid is obtained. The thicker mixturemay be thinned by adding more acetone. MISCELLANEOUS ITEMS. Making Square Bellows. The following information is given forthe instruction of those who wish to makebellows. In making square bellows firstcut out a pattern in paper, so that whenthe more expensive material is being used,it may be worked up with confidence andwithout
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